Thread-tension mechanism for sewing machines



Aug. 11,1936; R BECKER THREAD TENSIONMECHANKISM FOR SEWING MACHINES Filed April 2, 1935 2 sheets-sheet 1 Bzpdvvfi Becker Aug. 11, 1936. R. "BECKER THREAD TENSION MECHANISM FOR SEWING" MACHINES Filed April 2, 1935 2 Sheets-Sheet 2 Rudolpl Beckr Patented Aug. 11, 1936 UNITED STATES PATENT oFricE THREAD-TENSION MECHANISM FOR SEWING MACHINES Application April 2, 1935, Serial No. 14,218

8 Claims.

This invention relates to thread-tension mechanism for sewing machines, more particularly of the single-thread straw-braid-sewing type, such as represented in United States Patents No. 1,429,399, of Sept. 19, 1922; and No. 1,680,721, of Aug. 14, 1928. Machines of this type commonly employ hook and eye-pointed needles which are simultaneously projected upwardly through the work. Suitable looper devices above the work seize a loop of thread from the eye-pointed needle and present it to the hook-needle which pulls such loop downwardly through the work. The work is then fed a stitch-length by the usual feed-dog and, on the next upstroke of the needles, the eye-pointed needle passes through the loop of thread previously-pulled down by the hookneedle.

Machines of the type in question must be capable of sewing over a wide range of feed-adjustments varying, say, from a stitch-length of inch to a stitch-length of inch; thread-requirements for this variation in stitch-lengths running, roughly, from inch to 1% inches of thread per stitch. Various intermittent tension devices have heretofore been proposed to meet this wide variation in thread-requirements for the different stitch-lengths but none of them is sufliciently versatile to meet the wide range of sewing conditions met with in practice,

The present invention therefore has for an object to provide an intermittent tension mechanism which is capable of adjustment to meet sewing conditions .over a wide variety of materials and stitch-lengths. Another object of the invention is to provide an intermittent tension mechanism which is of compact construction and requires but little space within the machine bed for its installation. A further object of the invention is to provide a simplified intermittent threadtension mechanism the action of which is variable and is regulated by adjustment of the work-feeding mechanism. Still further, the invention has for an object to provide a variable intermittent tension mechanism which will function efiiciently at high speed over its entire range of adjustments. 7 With the above and other objects in View, as will hereinafter appear, the invention comprises the devices, combinations, and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of. the invention, from which the several features of the invention and the advantages attained thereby 'will be readily understood by those skilled in the art.

A feature of the invention, in one of its aspects, is the provision of a main cam functioning in the shortest stitch-length adjustment of the machine to hold the tension device open for the shortest length of time and the provision of a plurality of selectively controlled auxiliary cams which function individually to control the tension-device at other periods of the cycle when the main cam has ceased to function.

In the accompanying drawings, Fig. 1 is a transverse vertical section through the bed of a straw-braid sewing machine embodying the invention; the mechanism being set at the longest stitch-length adjustment. Fig. 2 is a similar view with the mechanism set at the shortest stitchlength adjustment. Fig. 3 is a plan view of the mechanism. Fig. 4'is a disassembled perspective view of the auxiliary cam-follower devices and the supporting means therefor which constitute a part of the present variable intermittent tension mechanism, and Fig. 5 is a detail view of the yoked end of the tension-control rod.

The machine, in general, is constructed substantially in accordance with the disclosure of the United Staees Patent No. 1,429,399, referred to. It includes the bed I ,cloth-plate 2, needles 3, feeddog 4 and main shaft 5. .The feed-dog 4 is mounted on the feed-bar 6 which is pivotally mounted at I on the feed-rocker 8 fulcrumed at 9 on the machine bed. V

The feed-lift mechanism is as usual and is preferably constructed substantially in accordance with the disclosure of United States Patent No. 1,397,071, of Nov. 15, 1921. Such mechanism includes a feed-lift link l0 pivotally connected at its upper end at H to the feed-bar 6 and at its lower end to a pin [2 receiving up-and-down movements from the main shaft through a suitable pitman l3 guided at its lower end in the slot M in the swivelled head l5.

The feed-bar 6 is given its feed-and-return movements by the usual forked pitman l6 pivotally connected at'll to the feed-rocker 8. The forked end of the pitman l6 embraces the usual cam-fol1ower block 18 surrounding the feed-eccentric IS on the main shaft 5. The pitman i6 is connected at 20 to one end of the anchor-link 2| the other end of which is connected at 22 to the feed-regulator lever 23 fulcrumed on the pin 2 journaled in the frame-lug 25. The feed-regulator lever 23 projects outwardly through the machine bed and has slidably mounted thereon a handle 26 influenced by the spring 21 to carry the detent teeth 28 at the base of the handle into a selected oneof the detent notches 29 in the rack-bar 30 secured to the bed I. In the ma.

chine illustrated there are five notches 29 in the rack-bar 30 which provide five predetermined stitch-length settings for the feed-regulator 23, evenly spaced from the longest stitch-length, Fig. 1, to the shortest stitch-length, Fig. 2.

The tension device comprises a seat 3| in the form of a cylindrical plug which is mounted in an aperture 32 in the bed I and is adjustably held in set position lengthwise of the axis of such aperture by the set-screw 33 bearing upon the fiat 33 extending lengthwise of the seat 3|. The seat 3! has a thread-tension face 34, Fig. 3. Slidabiy mounted in the seat 3| is the rod 35 the outer end-portion of which is reduced in diameter to form a shoulder 36. Freely mounted on the rod 35 between the shoulder 36 and a collar 3? screwed onto the reduced and screw-threaded end of the rod 35 is the tension-head 3B which is yieldingly urged toward the shoulder 36 by the spring 39 backed by the adjusting nut 40. The collar 37 may be adjusted or set at any desired distance from the shoulder 36 to provide a limited amount of play of the tension-head 38 lengthwise of the rod 35 between the shoulder 36 and collar 3?; a set-screw 31 holding the collar 31 in any position of adjustment.

The rod 35 is provided at its inner end with a yoke 4| which supports the pin 42 on which is journaled the roller 43; The yoke 4| has projecting portions 44 which are guided in slots 45 in the inner end of the seat 3| to maintain the axis of the roller 43 in parallelism with the main shaft 5. A relatively strong spring 4 3 reacting against the seat-member 3| urges the yoke 4| in a direction to close the tension-head 38 strongly against the face 34 of the tension-seat 3|.

Fixedly mounted on the main shaft is a nest of tension-release cams including a primary or main centrally disposed cam 41 and four differently and individually shaped auxiliary cams 4'! arranged two at either side of the primary cam 4'! which is larger in diameter than the auxiliary cams 41'.

The primary cam 41 acts directly upon the roller 43 to open the tension-device, whereas the auxiliary cams act upon the roller 43 through a group of follower bars 48 having thickened camengaged portions 49 arranged at individually different positions lengthwise of said bars. The cam-follower bars 48 are pivoted on the pin 50 carried by the lever 5| fulcrumed at 52 on the frame-lug 53. The lever 5| is formed between its ends with a slot 54 which is entered by the roller-stud 55 projecting laterally from the upward extension 55 of the feed-regulator lever When the feed-regulator lever is set with its handle 26 at its lowest position, Fig. 2, for production of the shortest stitch, the thread-requirements of the stitch-forming mechanism are at a minimum and the bars 48 are elevated to their highest point relative to the auxiliary cams 41, at which point all are inoperative as none of the thickened portions 49 is operatively engaged by an auxiliary cam 41'. This setting allows the primary cam 41 only to control the time of opening of the tension device. The high portion of the primary cam 41, which lies within the acute angle a--a, has a comparatively short angular extent of about 120 and is timed to fully open the tension-device as the rising needles enter the work and fully close the tension-device as the needles are nearing the end of their downstroke.

When the handle 26 is raised to the next higher notch 29 in the rack 30 to increase the stitchlength, the bar 48 having the lowest thickened portion 49 is selectively positioned for operative engagement by its respective auxiliary cam 4'1, shown in section in Fig. 2, the function of which is not to open the tension-device any wider than it would be opened by the primary cam 41, but to prolong the time the tension is held open; the high portion of the auxiliary cam between the points, 17, c functioning to hold the tension open for a short time after it would have been allowed to close by the primary cam 47 functioning alone. i

It will be obvious that for each stitch-length adjustment a selection is made of one or another of the follower bars 48 which is operatively positioned relative to its respective cam 41 for the control of the tension-device.

While in the specific embodiment of the invention shown and described, the individual actions of the auxiliary cams cannot encroach upon the tension-opening action of the primary cam,

they can selectively prolong the time the tension is to remain opento meet the thread-requirements of the particular stitch-length adjustment. By omitting the primary cam and the shortest stitchlength adjustment, it is possible to have a plurality of independent tension-controlling cams which are selectively controlled by the feed-adjustment and the action of each of which is quite independent of the others.

By adjusting the collar 31' toward or away from the shoulder 36 on the rod 35, and by adjusting the seat 3| in the aperture 32, it is possible to allow the tension device to close with a light tension or with a strong tension, or to vary from a light tension to a strong tension without opening at all. The provision of these adjustments increases the range of usefulness of the device to meet a wide variety of sewing conditions met with in practice, as will be readily understood by those skilled in the art.

Having thus set forth the nature of the invention, what I claim herein is:

1. In a sewing machine, the combination with a rotary shaft and feeding mechanism including a four-motion feed-dog and a feed-regulator, of a spring-closed thread-tension device, a plurality of cams fixed on said shaft, and means connected to said feed-regulator for rendering any desired one of said cams operative upon said tension-device.

2. An intermittent thread-tension for sewing machines including a spring-closed tension-device, a rotary shaft, a nest of tension-opening cams on said shaft, a plurality of cam-follower interponents arranged each between a respective one of said cams and said tension-device, and selectively controlled means for shifting said interponents to carry any desired one of them into operative relation with its respective cam and said tension device.

3. An intermittent thread-tension for sewing machines including a spring closed tension-device, a rotary shaft, a primary tension-controlling cam on said shaft, an auxiliary tension-controlling cam on said shaft, and an interponent between said auxiliary cam and tension-device shiftable from an operative to an inoperative position.

4. An intermittent thread-tension for sewing machines including a spring closed tension-device, a rotary shaft, a primary tension-controlling cam on said shaft, an auxiliary tensioncontrolling cam on said shaft, and an interponent between said cam and tension-device shiftable from an operative to an inoperative position,

said interponent being in the form of an endwise movable bar having a thickened operative cam-follower portion.

5. An intermittent thread-tension for sewing machines including a spring-closed tensiondevice, a rotary shaft, a nest of tension-controlling cams on said shaft, a plurality of cam-follower interponents arranged each between a respective one of said cams and said tension-device, said interponents being each in the form of an endwise shiftable bar having a thickened camfollower portion, said thickened portions being at different positions endwise of said bars, and means for shifting said bars endwise to render a desired one of said interponents operative.

6. An intermittent tension-device for sewing machines comprising a tension-seat, a tensionhead, an endwise movable rod passing through said seat and head, spaced shoulders on said rod between which said head has a limited movement lengthwise of and, relative to said rod, a relatively strong spring for moving said rod in a direction to carry said head toward said seat, a relatively weak spring carried by said rod and applied to said head to yieldingly urge the latter toward said seat, and a tension-controlling cam for moving said rod endwise in opposition to said strong spring.

7. An intermittent thread-tension device comprising, a frame including a tension-seat, an

' endwise movable rod passing through said seat and having fixed and adjustable shoulders thereon, a tension-head disposed on said rod and movable lengthwise of said rod between said shoulders, a spring carried by said rod and applied to said tension-head, and a second spring applied to said rod to move the latter in a direction to carry said tension-head toward said tension-seat.

8. An intermittent thread-tension for sewing machines including a tension-device, a rotary shaft, a nest of tension-operating cams fixed on said shaft, and means, movable at the will of the operator and shiftably interposed between said cams and said tension-device, to render any selected one of said cams operative upon said tension device.

RUDOLPH BECKER. 

